Elemental sulfur has found wide application in a number of industries. primarily the agricultural and chemical industries as, for example, a soil amendment, a crop pesticide, a chemical precursor, e.g., sulfuric acid, in rubber compounding, and, more recently, in the fabrication of road surface and structural material compounds. Sulfur can be shipped in molten or crushed block form, or as particles such as those disclosed in my U.S. Pat. No. 3,637,351, 3,769,378 and 3,880,361. These and other forms of sulfur obviously have different physical properties. They may or may not be adulterated with materials to which they are exposed during manufacture or recovery.
One combination of physical properties and structure will not be the best for all uses. For example, in some instances it may be preferable to minimize particle comminution and dusting in shipment, storage or use. Conversely, particles of lower attrition resistance might be preferred over hard particles when the end use involves conversion of the sulfur to a finely divided form such as beads or powders suitable as soil or compounding sulfurs. In the latter case the user would obviously prefer a sulfur which requires little energy to comminute and less expensive light duty equipment. On the other hand, some users are less concerned with the energy requirements than they are with dusting and the difficulties involved in handling finely divided sulfurs.
Hence, it would be advantageous to consistently produce sulfur particles of either high or low relative attribution resistance as dictated by the user's preference. I have now discovered that this objective can be achieved in the manufacture of crystalline particle-form sulfurs having diameters less than about 0.5 inch, and which are obtained by crystallizing fused sulfur in an inert liquid medium.
It is therefore one object of this invention to provide an improved method for producing crystalline alpha-sulfur particles. Another object is the provision of an improved method for producing crystalline sulfur particles which can be easily crushed or otherwise abraded to form finely divided sulfurs. It is another object to provide an improved method for controlling the relative attrition resistance of sulfur particles formed by crystallizing fused sulfur in an agitated liquid medium. Another object is the provision of a method for consistently producing solid sulfur particles having either high or low relative attrition resistance as desired.
These and other objects and aspects of this invention will be apparent to one skilled in the art in view of the embodiments and claims hereof.
In accordance with one embodiment the relative attrition resistance of alpha-sulfur particles formed by shock-crystallizing molten sulfur in a continuous, agitated liquid phase, is controlled by controlling the temperature of the fused sulfur immediately prior to crystallization, and the quenching temperature gradient. Quenching temperature gradient is a function of the temperature gradient through which the molten sulfur is quenched defined by the temperature difference between the fused sulfur and quench medium. Briefly, I have found that higher fused sulfur temperatures and higher quenching temperature gradients produce harder alpha-sulfur particles, and that, accordingly, particles of desired hardness can be consistently obtained by controlling these dominating parameters. While fused sulfur temperature is by far the most significant and, for that matter, the most flexible control variable, it appears that quenching temperature differential also influences attrition resistance, at least to some extent.